The Scientist - USA (2020-04)

40 THE SCIENTIST | the-scientist.com

M

athilde was diagnosed with

breast cancer at the age

of 44. Doctors treated her

with surgery, chemother-

apy, and radiation, and Mathilde’s physi-

cian informed her that, among many other

side effects of her cancer treatment, she

could expect to lose muscle mass. To fight

muscle wasting, Mathilde began the inten-

sive physical training program offered to

cancer patients at the Rigshospitalet Uni-

versity Hospital of Copenhagen. The pro-

gram consists of 3.5-hour sessions of com-

bined resistance and aerobic training, four

times a week for six weeks. Although the

chemotherapy made her tired, Mathilde

(a friend of mine, not pictured, who

requested I use her first name only) did

not miss a single training session.

“In a way it felt counterintuitive to

do intensive, hard training, while I was

tired and nauseous, but I was convinced

that the training was good for my physi-

cal and mental health and general well-

being,” Mathilde told me in Danish.

She followed the chemo- and radio-

therapy strictly according to the pre-

scribed schedule. She was not hospi-

talized, acquired no infections, and did

not develop lymphedema, a failure of

the lymphatic system that commonly

occurs following breast cancer surgery

and leads to swelling of the limbs.

Physical exercise is increasingly

being integrated into the care of cancer

patients such as Mathilde, and for good

reason. Evidence is accumulating that

exercise improves the wellbeing of these

patients by combating the physical and

mental deterioration that often occur

during anticancer treatments. Most

remarkably, we are beginning to under-

stand that exercise can directly or indi-

rectly fight the cancer itself.

An increasing amount of epidemio-

logical literature strongly indicates that

exercise training may lower the risk of

cancer, control disease progression,

amplify the effects of anticancer ther-

apy, and improve physical function and

psychosocial outcomes. For example, a

2016 study of more than 1.4 million indi-

viduals in the US and Europe found that

people could reduce their cancer risk

with moderate to vigorous leisure-time

exercise training. The phenomenon held

across several different cancers, includ-

ing breast, colon, rectum, esophagus,

lung, liver, kidney, bladder, and head

and neck.^1 And the combined results

of approximately 700 unique exercise

intervention trials, involving more than

50,000 cancer patients in total, leave

little doubt that patients benefit from

physical activity, showing improvements

such as reduced toxicity of anticancer

treatment, decreased disease progres-

sion, and enhanced survival. The same

studies showed that exercise training

improves mood, decreases loss of muscle

mass, and helps cancer patients return to

work earlier after successful treatment.^2

Some studies show that 150 minutes per

week of moderate exercise nearly dou-

ble the chance of survival compared with

breast cancer patients who don’t exercise

during treatment.^3

Hundreds of animal studies, con-

ducted over decades, suggest that the

link is likely causal: in mice and rats,

exercise leads to a reduction in the

incidence, growth rate, and metastatic

potential of cancer across a large vari-

ety of models of different human and

murine tumor types. But how exercise

helps fight cancer is a bit of a black box.

Exercise may improve the efficacy of

anticancer treatment by boosting the

immune system and thereby attenuating

the toxicity of chemotherapy and immu-

notherapy. Cancer patients are also

likely to benefit from the overall health-

promoting properties of physical activ-

i ty, such as improved metabolism and

enhanced cardiovascular function.

Uncovering the mechanisms whereby

exercise induces anticancer effects is

crucial to fighting the disease. Exercise-

related factors that have a direct or

indirect anticancer effect could serve as

valuable biomarkers for monitoring the

amount, intensity, and type of exercise

required to best aid cancer treatment.

Such research could also potentially

highlight novel therapeutic targets.

Each workout matters

Regardless of the nature of the train-

ing, the primary setting of exercise’s

effect on cancer is the bloodstream.

Long-term training has been associ-

ated with a reduction in the blood lev-

els of systemic risk factors, such as

OUTRUNNING CANCER: Tumors on the lungs

of sedentary mice (left) and animals that ran

on wheels (right) after injection with melanoma cells.

L. PEDERSEN ET AL.,

CELL

METAB

,^2016